Systems and methods for over-temperature protection and over-voltage protection for power conversion systems

ABSTRACT

Systems and methods are provided for protecting a power conversion system. A system controller includes a first controller terminal and a second controller terminal. The first controller terminal is configured to provide a drive signal to close and open a switch to affect a first current flowing through a primary winding of a power conversion system. The second controller terminal is configured to receive first input signals during one or more first switching periods and receive second input signals during one or more second switching periods. The system controller is configured to determine whether a temperature associated with the power conversion system is larger than a predetermined temperature threshold, and in response to the temperature associated with the power conversion system being larger than the predetermined temperature threshold, generate the drive signal to cause the switch open and remain open to protect the power conversion system.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/075,303, filed Nov. 8, 2013, which claims priority to Chinese PatentApplication No. 201310450298.1, filed Sep. 26, 2013, both of theabove-identified applications being commonly assigned and incorporatedby reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for systemprotections. Merely by way of example, the invention has been applied toover-temperature protection and over-voltage protection of powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

Power conversion systems are often used in many electronic devices toprovide power for the electronic devices to operate properly. To protectthe electronic devices from being damaged under certain circumstances,many power conversion systems usually include certain protectionmechanisms, such as over-temperature protection (OTP) and over-voltageprotection (OVP). Oftentimes, a controller chip of a power conversionsystem uses two different terminals (e.g., pins) for OTP and OVPrespectively. In certain controller chips, a terminal is used for OTP,and another terminal for current sensing (e.g., a CS terminal) is usedfor OVP. But the related OVP detection circuit may disturb the currentsensing mechanism. In some controller chips, a single terminal (e.g., apin) may be selected to perform OTP or selected to perform OVP, butcannot be selected to perform both OTP and OVP.

FIG. 1 is a simplified conventional diagram for over-temperatureprotection of a power conversion system. The power conversion system 10includes a controller 12, a primary winding 14, a secondary winding 16,an auxiliary winding 18, a switch 20, resistors 22 and 24, diodes 26 and28, capacitors 30 and 32, and a feedback component 34. The controller 12includes terminals (e.g., pins) 36, 38, 40, 42, 44 and 46. For example,the switch 20 includes a field effect transistor. In another example,the switch 20 includes a bipolar junction transistor. In yet anotherexample, the switch 20 includes an insulated-gate bipolar transistor.

As shown in FIG. 1, the resistor 22 is coupled to the terminal 36 (e.g.,terminal OTP) for OTP detection. For example, the resistor 22 is athermal resistor (e.g., a thermistor) that changes its resistance withtemperature. As an example, the resistor 22 has a negative temperaturecoefficient, i.e., the resistance of the resistor 22 decreases withincreasing temperatures. When the temperature of the power conversionsystem 10 is higher than a threshold temperature (e.g., T₀), theresistance of the resistor 22 becomes smaller than a thresholdresistance (e.g., R₀), in some embodiments. For example, if a current 48(e.g., I_(OTP)) flowing through the resistor 22 does not change inmagnitude with temperature, a voltage drop across the resistor 22 isdetermined as follows:V _(RT) =I _(OTP) ×R ₀  (Equation 1)If the voltage drop across the resistor 22 is smaller in magnitude thana predetermined reference voltage, it is determined that the temperatureof the power conversion system 10 is too high. For example, if thevoltage drop across the resistor 22 remains smaller in magnitude thanthe predetermined reference voltage during a predetermined time period(e.g., N clock cycles), the OTP mechanism is triggered and thecontroller 12 changes a drive signal 50 to open (e.g., turn off) theswitch 20 in order to power off the power conversion system 10. But thecontroller 12 cannot perform OTP detection and OVP detection using asingle terminal (e.g., terminal 36).

The controller 12 includes no additional terminals other than the sixterminals (e.g., the six pins) 36, 38, 40, 42, 44, and 46. For example,the terminal 38 (e.g., terminal V_(CC)) is used to receive a supplyvoltage for the controller 12, and the terminal 44 (e.g., terminal CS)is used to receive a current-sensing signal associated with a primarycurrent flowing through the primary winding 14. In another example, theterminal 42 (e.g., terminal GND) is biased at a ground voltage, and theterminal 40 (e.g., terminal GATE) is used to output the drive signal toopen (e.g., turn off) and/or close (e.g., turn on) the switch 20.Alternatively, the controller 12 includes one or more additionalterminals (e.g., one or more additional pins) other than the sixterminals (e.g., the six pins) 36, 38, 40, 42, 44, and 46.

Hence it is highly desirable to improve the technique for achieving OTPand OVP in power conversion systems.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for systemprotections. Merely by way of example, the invention has been applied toover-temperature protection and over-voltage protection of powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

According to one embodiment, a system controller for protecting a powerconversion system includes, a first controller terminal configured toprovide a drive signal to close and open a switch to affect a firstcurrent flowing through a primary winding of a power conversion system,the drive signal being associated with one or more switching periodsincluding one or more first switching periods and one or more secondswitching periods, and a second controller terminal configured toreceive one or more first input signals during the one or more firstswitching periods and receive one or more second input signals duringthe one or more second switching periods. The system controller isconfigured to, process information associated with the first inputsignals, determine whether a temperature associated with the powerconversion system is larger than a predetermined temperature thresholdbased on at least information associated with the first input signals,and in response to the temperature associated with the power conversionsystem being larger than the predetermined temperature threshold,generate the drive signal to cause the switch open and remain open toprotect the power conversion system. The system controller is furtherconfigured to, process information associated with the second inputsignals, determine whether an output voltage associated with a secondarywinding of the power conversion system is larger than a predeterminedvoltage threshold based on at least information associated with thesecond input signals, and in response to the output voltage associatedwith the secondary winding of the power conversion system being largerthan the predetermined voltage threshold, generate the drive signal tocause the switch to open and remain open to protect the power conversionsystem.

According to another embodiment, a system for protecting a powerconversion system includes, a system controller including a firstcontroller terminal configured to provide a drive signal to close andopen a switch to affect a first current flowing through a primarywinding of a power conversion system, and a second controller terminalconfigured to receive one or more input signals, the power conversionsystem further including a secondary winding and an auxiliary winding,the primary winding coupled to the secondary winding, a first resistorincluding a first resistor terminal and a second resistor terminal, thefirst resistor terminal being coupled to the second controller terminal,one or more first diodes including a first diode terminal and a seconddiode terminal, a first diode terminal being coupled to the secondcontroller terminal, and a second resistor including a third resistorterminal and a fourth resistor terminal, the third resistor terminalbeing coupled to the second diode terminal. The second resistor terminalis configured to receive an output signal associated with the auxiliarywinding coupled to the secondary winding.

According to yet another embodiment, a system controller for protectinga power conversion system includes, a first controller terminalconfigured to provide a drive signal to close and open a switch toaffect a first current flowing through a primary winding of a powerconversion system, the drive signal being associated with one or moreswitching periods including a first switching period and a secondswitching period; and a protection component configured to receive afirst voltage signal associated with a first input current flowingthrough a resistor during the first switching period and receive asecond voltage signal associated with a second input current flowingthrough the resistor during the second switching period, the first inputcurrent and the second input current being different in magnitude. Theprotection component is further configured to, in response to adifference between the first voltage signal and the second voltagesignal being larger than a predetermined threshold in magnitude, outputa protection signal to generate the drive signal to cause the switch toopen and remain open to protect the power conversion system.

According to yet another embodiment, a system controller for protectinga power conversion system includes, a first controller terminalconfigured to receive an input current, a first resistor configured toreceive a first current and the input current and generate a firstvoltage based on at least information associated with the first currentand the input current, a second resistor configured to receive a secondcurrent and generate a second voltage based on at least informationassociated with the second current, and a processing componentconfigured to, in response to the first voltage becoming larger than afirst voltage threshold in magnitude, increase the second voltage inmagnitude, discharge a capacitor coupled to the processing component,and decrease a third voltage in magnitude associated with the capacitor.

In one embodiment, a method for protecting a power conversion systemincludes, providing a drive signal to close and open a switch to affecta first current flowing through a primary winding of a power conversionsystem, the drive signal being associated with one or more switchingperiods including one or more first switching periods and one or moresecond switching periods, receiving one or more first input signalsduring the one or more first switching periods, processing informationassociated with the one or more first input signals, and determiningwhether a temperature associated with the power conversion system islarger than a predetermined temperature threshold based on at leastinformation associated with the one or more first input signals. Themethod further includes, in response to the temperature associated withthe power conversion system being larger than the predeterminedtemperature threshold, generating the drive signal to cause the switchopen and remain open to protect the power conversion system, receivingone or more second input signals during the one or more second switchingperiods, processing information associated with the one or more secondinput signals, determining whether an output voltage associated with asecondary winding of the power conversion system is larger than apredetermined voltage threshold based on at least information associatedwith the one or more second input signals, and in response to the outputvoltage associated with the secondary winding of the power conversionsystem being larger than the predetermined voltage threshold, generatingthe drive signal to cause the switch to open and remain open to protectthe power conversion system.

In another embodiment, a method for protecting a power conversion systemincludes, providing a drive signal to close and open a switch to affecta first current flowing through a primary winding of a power conversionsystem, the drive signal being associated with one or more switchingperiods including a first switching period and a second switchingperiod, receiving a first voltage signal associated with a first inputcurrent flowing through a resistor during the first switching period,receiving a second voltage signal associated with a second input currentflowing through the resistor during the second switching period, thefirst input current and the second input current being different inmagnitude, and in response to a difference between the first voltagesignal and the second voltage signal being larger than a predeterminedthreshold in magnitude, outputting a protection signal to generate thedrive signal to cause the switch to open and remain open to protect thepower conversion system.

In yet another embodiment, a method for protecting a power conversionsystem includes, receiving an input current and a first current,processing information associated with the input current and the firstcurrent, and generating a first voltage based on at least informationassociated with the first current and the input current. The methodadditionally includes, receiving a second current, processinginformation associated with the second current, and generating a secondvoltage based on at least information associated with the secondcurrent. The method further includes, in response to the first voltagebecoming larger than a first voltage threshold in magnitude, increasingthe second voltage in magnitude, discharging a capacitor, and decreasinga third voltage in magnitude associated with the capacitor.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified conventional diagram for over-temperatureprotection of a power conversion system.

FIG. 2 is a simplified diagram for over-temperature protection andover-voltage protection of a power conversion system using one terminalaccording to one embodiment of the present invention.

FIG. 3 is a simplified diagram for a controller as part of a powerconversion system as shown in FIG. 2 according to one embodiment of thepresent invention.

FIG. 4 is a simplified diagram showing certain components of a powerconversion system as shown in FIG. 2 according to one embodiment of thepresent invention.

FIG. 5 is a simplified timing diagram for a power conversion system asshown in FIG. 2 according to one embodiment of the present invention.

FIG. 6 is a simplified diagram showing certain components of anover-temperature-protection detector as part of a detection component ina controller as shown in FIG. 2 according to one embodiment of thepresent invention.

FIG. 7 is a simplified diagram showing certain components of anover-voltage-protection detector as part of a detection component in apower conversion system as shown in FIG. 2 according to one embodimentof the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for systemprotections. Merely by way of example, the invention has been applied toover-temperature protection and over-voltage protection of powerconversion systems. But it would be recognized that the invention has amuch broader range of applicability.

The fabrication cost of a controller chip may increase if differentterminals (e.g., pins) are assigned for OTP and OVP respectively. Inaddition, it is difficult to enclose two separate terminals (e.g., pins)for OTP and OVP in certain chip packaging. But the single terminal maynot be used to achieve both OTP and OVP simultaneously.

FIG. 2 is a simplified diagram for over-temperature protection andover-voltage protection of a power conversion system using one terminalaccording to one embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The power conversion system 100 includes a controller 102, a primarywinding 104, a secondary winding 106, an auxiliary winding 108, a switch110, resistors 112, 114 and 118, diodes 116, 124 and 126, capacitors 122and 128, and a feedback component 120. The controller 102 includesterminals (e.g., pins) 130, 132, 134, 136, 138 and 140. For example, theswitch 110 includes a field effect transistor. In another example, theswitch 110 includes a bipolar junction transistor. In yet anotherexample, the switch 110 includes an insulated-gate bipolar transistor.The diode 116 is replaced with a number of diodes connected in series,in some embodiments. As an example, the auxiliary winding 108 is coupledto the secondary winding 106. In another example, the primary winding104 is coupled to the secondary winding 106.

According to one embodiment, a transformer including the primary winding104 and the secondary winding 106 is used to isolate an input voltage196 on the primary side and an output voltage 198 on the secondary side.For example, the feedback component 120 transmits a feedback signal 144associated with the output voltage 198 from the secondary side to theterminal 136 (e.g., terminal FB) of the controller 102. As an example,the feedback component 120 includes TL431 and an opto-coupler. When theswitch 110 is closed (e.g., being turned on), energy is stored in theprimary winding 104, and when the switch 110 is opened (e.g., beingturned off), the energy stored in the primary winding 110 is released tothe secondary side, in some embodiments.

According to another embodiment, the terminal 130 of the controller 102is used to achieve both over-temperature protection (OTP) andover-voltage protection (OVP). For example, during a first time period(e.g., a switching period), the terminal 130 is configured to receive afirst input signal, and whether the OTP mechanism is triggered isdetermined based on at least information associated with the first inputsignal. In another example, and during a second time period (e.g.,another switching period) that is different from the first time period,the terminal 130 is configured to receive a second input signal, andwhether the OVP mechanism is triggered is determined based on at leastinformation associated with the second input signal.

As shown in FIG. 2, the terminal 130 is connected to the resistor 114and the diode 116 (e.g., the anode) and the resistor 118 (e.g., R_(T))is connected to the diode 116 (e.g., the cathode), in some embodiments.For example, the resistor 114 is configured to receive a voltage signal142 from the auxiliary winding 108. As an example, the voltage signal142 maps the output voltage 198. In another example, the resistor 118 isa thermal resistor (e.g., a thermistor) that changes its resistance withtemperature. In yet another example, the resistor 118 has a negativetemperature coefficient, i.e., the resistance of the resistor 118decreases with increasing temperatures.

In certain embodiments, if the temperature of the power conversionsystem 100 exceeds a temperature threshold, the OTP is triggered, andthe controller 102 outputs, at the terminal 134 (e.g., terminal GATE), adrive signal 146 to open (e.g., turn off) the switch 110. For example,the power conversion system 100 is shut down and the switch 110 keepsopen. In another example, after being shut down, the system 100 restarts(e.g., automatically or manually) and starts modulation again. In yetanother example, the switch 110 keeps open for a first predeterminedtime period that is larger in duration than a switching period of thesystem 100.

In some embodiments, if the voltage signal 142 exceeds a voltagethreshold, the OVP is triggered, and the controller 102 outputs thedrive signal 146 to open (e.g., turn off) the switch 110. For example,the power conversion system 100 is shut down and the switch 110 keepsopen. In another example, after being shut down, the system 100 restarts(e.g., automatically or manually) and starts modulation again. In yetanother example, the switch 110 keeps open for a second predeterminedtime period that is larger in duration than a switching period of thesystem 100.

The controller 102 includes no additional terminals other than the sixterminals (e.g., the six pins) 130, 132, 134, 136, 138 and 140 in someembodiments. For example, the terminal 132 (e.g., terminal V_(CC)) isused to receive a supply voltage for the controller 102, and theterminal 138 (e.g., terminal CS) is used to receive a current-sensingsignal associated with a primary current flowing through the primarywinding 104. In another example, the terminal 140 (e.g., terminal GND)is biased at a ground voltage, and the terminal 134 (e.g., terminalGATE) is used to output the drive signal 146 to open (e.g., turn off)and/or close (e.g., turn on) the switch 110. In certain embodiments, thecontroller 102 includes one or more additional terminals (e.g., one ormore additional pins) other than the six terminals (e.g., the six pins)130, 132, 134, 136, 138 and 140.

FIG. 3 is a simplified diagram for the controller 102 as part of thepower conversion system 100 according to one embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications.

The controller 102 includes a detection component 202, OR gates 206 and230, an oscillator 212, a logic controller 214, a flip-flop component216, and a driving component 218. In addition, the controller 102includes a PK/Green/Burst component 220, a slope-compensation component222, a leading-edge-blanking (LEB) component 224, comparators 226 and228, an under-voltage lock-out (UVLO) component 232, a reference-signalgenerator 234, and resistors 236, 238 and 240. In certain embodiments,the OR gate 206 is included in the logic controller 214.

According to one embodiment, the terminal 130 (e.g., terminal P1)provides one or more input signals to the detection component 202 whichgenerates an OTP-detection signal 208 and an OVP-detection signal 210 tothe OR gate 206. For example, the OR gate 206 outputs a signal 242 tothe logic controller 214 to affect the status of the switch 110.

Whether the OVP mechanism is triggered is determined based on at leastinformation associated with a current 188 (e.g., I_(OVP)) flowingthrough the resistor 114, in certain embodiments. For example, if thecurrent 188 becomes larger in magnitude than a threshold current, it isdetermined that the output voltage of the power conversion system 100 istoo high. As an example, if the current 188 keeps larger in magnitudethan the threshold current during another predetermined time period(e.g., M clock cycles), the OVP mechanism is triggered and thecontroller 102 changes the drive signal 146 to open (e.g., turn off) theswitch 110 in order to power off the power conversion system 100. Insome embodiments, the diode 116 serves to reduce a leakage currentflowing from the resistor 118 toward the terminal 130 (e.g., terminalP1) during the OVP detection. In addition, a voltage 184 (e.g., V₁)associated with the terminal 130 (e.g., terminal P1) is keptapproximately smaller in magnitude than a turn-on voltage (e.g., aforward voltage) of the diode 116.

FIG. 4 is a simplified diagram showing certain components of the powerconversion system 100 according to one embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 4, the detection component 202 includes current-source components302 and 304, switches 306, 308, 310, 312 and 314, an OTP detector 316,and an OVP detector 318.

According to one embodiment, the switches 306 and 312 are closed oropened in response to a switching signal 320 (e.g., S₀), and theswitches 308 and 310 are closed or opened in response to a switchingsignal 322 (e.g., S₁). For example, the switch 314 is closed or openedin response to a switching signal 324 (e.g., S_(ovp)). The OVP detectionand the OTP detection are performed during different switching periodsby controlling the switches 306, 308, 310, 312 and 314 in someembodiments.

FIG. 5 is a simplified timing diagram for the power conversion system100 according to one embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The waveform 402 representsthe drive signal 146 as a function of time, the waveform 404 representsthe switching signal 324 (e.g., S_(ovp)) as a function of time, thewaveform 406 represents the switching signal 320 (e.g., S₀) as afunction of time, and the waveform 408 represents the switching signal322 (e.g., S₁) as a function of time. The OVP detection and the OTPdetection are performed alternately during different switching periodsin certain embodiments.

Three switching periods are shown in FIG. 5, T₁, T₂, and T₃. Theswitching period T₁ starts at time t₀ and ends at time t₂, the switchingperiod T₂ starts at the time t₂ and ends at time t₄, and the switchingperiod T₃ starts at the time t₄ and ends at time t₆. In addition, withinthe first switching period T₁, a time period T_(S0) starts at the timet₀ and ends at time t₁. A time period T_(OVP) within the secondswitching period T₂ starts at the time t₂ and ends at time t₃. Further,a time period T_(S1) within the third switching period T₃ starts at thetime t₄ and ends at time t₅. For example, t₀≤t₁≤t₂≤t₃≤t₄≤t₅≤t₆. As shownin FIG. 5, the OTP detection is performed during the switching period T₁and T₃, and the OVP detection is performed during the switching periodT₂.

As shown in FIG. 4 and FIG. 5, at the beginning of the switching periodT₁ (e.g., at t₀), the drive signal 146 changes from a logic high levelto a logic low level, and the switch 110 is opened (e.g., being turnedoff), according to one embodiment. For example, the switching signal 320(e.g., S₀) changes from the logic low level to the logic high level andkeeps at the logic high level during the time period T_(S0) (e.g., untilt₁), and the switches 306 and 312 are closed (e.g., being turned on). Asan example, the current-source component 302 provides a current 330(e.g., I_(OTP0)) for OTP detection.

According to another embodiment, at the beginning of the switchingperiod T₂ (e.g., at t₂), the drive signal 146 changes from the logichigh level to the logic low level, and the switch 110 is opened (e.g.,being turned off). As an example, the voltage signal 142 is related tothe output voltage 198 when the drive signal 146 is at the logic lowlevel. For example, the switching signal 324 (e.g., S_(ovp)) changesfrom the logic low level to the logic high level and keeps at the logichigh level during the time period T_(OVP) (e.g., until t₃), and theswitch 314 is closed (e.g., being turned on). In another example, thecurrent 188 flows through the resistor 114 and the terminal 130 (e.g.,terminal P1), and is received by the OVP detector 318 for OVP detection.

According to yet another embodiment, at the beginning of the switchingperiod T₃ (e.g., at t₄), the drive signal 146 changes from the logichigh level to the logic low level, and the switch 110 is opened (e.g.,being turned off). For example, the switching signal 322 (e.g., S₁)changes from the logic low level to the logic high level and keeps atthe logic high level during the time period T_(S1) (e.g., until t₅), andthe switches 308 and 310 are closed (e.g., being turned on). As anexample, the current-source component 304 provides a current 328 (e.g.,I_(OTP1)) for OTP detection.

In one embodiment, the OTP detection is achieved based on at leastinformation associated with the voltage signal 184. For example, thecurrent 188 (e.g., I_(OVP)) is determined as follows:

$\begin{matrix}{I_{OVP} = \frac{V_{o} - V_{1}}{R_{OVP}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$where V_(o) represents the voltage signal 142, V₁ represents the voltagesignal 184, and R_(OVP) represents the resistance of the resistor 114.As an example, the voltage signal 184 is determined as follows:V ₁ =V _(D)+(I _(OVP) +I _(OTP))×R _(T)  (Equation 3)where V_(D) represents a turn-on voltage (e.g., a forward voltage) ofthe diode 116, I_(OTP) represents the current 186, and R_(T) representsthe resistance of the resistor 118.

Combining Equation 2 and Equation 3, the voltage signal 184 isdetermined as follows:

$\begin{matrix}{V_{1} = {{\frac{R_{OVP}}{R_{OVP} + R_{T}} \times V_{D}} + {\frac{R_{T}}{R_{OVP} + R_{T}} \times V_{o}} + {\frac{R_{T} \times R_{OVP}}{R_{OVP} + R_{T}} \times I_{OTP}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

Assuming the turn-on voltage (e.g., a forward voltage) of the diode 116does not change with the current 186, a change of the voltage signal 184between different time periods for OTP detection is determined asfollows, according to certain embodiments:

$\begin{matrix}{{\Delta\; V_{1}} = {{{V_{1}\left( S_{0} \right)} - {V_{1}\left( S_{1} \right)}} = {\frac{R_{T} \times R_{OVP}}{R_{OVP} + R_{T}} \times \Delta\; I_{OTP}}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$where V₁(S₀) represents a magnitude of the voltage signal 184 during thetime period T_(S0), V₁(S₁) represents a magnitude of the voltage signal184 during the time period T_(S1), and ΔI_(OTP) represents a change ofthe current 186 between the time periods T_(S0) and T_(S1). For example,the change of the current 186 between the time periods T_(S0) and T_(S1)is determined as follows:ΔI _(OTP) =I _(OTP0) −I _(OTP1)  (Equation 6)where I_(OTP0) represents the current 330, and I_(OTP1) represents thecurrent 328.

As discussed above and further emphasized here, FIG. 4 and FIG. 5 aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, the time period T_(OVP)precedes both the time period T_(S0) and the time period T_(S1). Inanother example, the time period T_(OVP) follows both the time periodT_(S0) and the time period T_(S1). In yet another example, the switchingperiod T₃ that includes the time period T_(S1) immediately follows theswitching period T₁ that includes the time period T_(S0). In yet anotherexample, the switching period T₁ that includes the time period T_(S0)follows immediately the switching period T₃ that includes the timeperiod T_(S1). In yet another example, the switching period T₃ thatincludes the time period T_(S1) is separated from the switching periodT₁ that includes the time period T_(S0) by one or more switchingperiods. In yet another example, the switching period T₂ that includesthe time period T_(OVP) immediately follows the switching period T₃ thatincludes the time period T_(S1). In yet another example, the switchingperiod T₂ that includes the time period T_(OVP) is separated from theswitching period T₁ that includes the time period T_(S0) by one or moreswitching periods. In yet another example, the switching period T₂ thatincludes the time period T_(OVP) is separated from the switching periodT₃ that includes the time period T_(S1) by one or more switchingperiods.

FIG. 6 is a simplified diagram showing certain components of the OTPdetector 316 as part of the detection component 202 in the controller102 according to one embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 6, the OTPdetector 316 includes switches 502 and 508, capacitors 504 and 506, acomparator 510, an amplifier 512, and a counter component 514. Forexample, the switches 502 and 508 are closed or opened in response tothe switching signal 320 (e.g., S₀).

According to one embodiment, during the first time period (e.g., thetime period T_(S0)), when the switch 312 is closed, the capacitor 506 ischarged in response to the voltage signal 184 until a voltage 516received at an inverting terminal (e.g., the “−” terminal) of thecomparator 510 is approximately equal in magnitude to the voltage signal184. For example, the voltage signal 184 is sampled at the capacitor506. In another example, the amplifier 512 receives a reference signal518 (e.g., V_(REF)) at a non-inverting terminal (e.g., the “+”terminal). In yet another example, the switches 502 and 508 are closed(e.g., being turned on) in response to the switching signal 320, and theswitch 310 is opened (e.g., being turned off) in response to theswitching signal 322. As an example, the capacitor 504 is charged untila voltage 520 received at a non-inverting terminal (e.g., the “+”terminal) of the comparator 510 is approximately equal in magnitude tothe reference signal 518.

According to another embodiment, during a second time period (e.g., thetime period T_(S1)), when the switch 310 is closed, the switches 312,502 and 508 are opened (e.g., being turned off) in response to theswitching signal 320. For example, a voltage 522 at a terminal of thecapacitor 504 is approximately equal in magnitude to the voltage signal184. In another example, the other terminal of the capacitor 504 isfloating, and the voltage 520 at the non-inverting terminal of thecomparator 510 is determined as follows:V _(A) =V _(REF) +V ₁(S ₁)  (Equation 7)where V_(REF) represents the reference signal 518, and V₁(S₁) representsthe voltage signal 184 during the second time period. In yet anotherexample, the voltage 516 at the inverting terminal of the comparator 510is kept at approximately the voltage signal 184 during the first timeperiod.

According to yet another embodiment, when the voltage 520 is larger inmagnitude than the voltage 516 as follows:V ₁(S ₀)−V ₁(S ₁)<V _(REF)  (Equation 8)where V₁(S₀) represents the voltage signal 184 during the first timeperiod, and V₁(S₁) represents the voltage signal 184 during the secondtime period, it indicates that the temperature of the power conversionsystem 100 is higher than a temperature threshold. For example, thecomparator 510 generates a signal 524 at a logic high level. In anotherexample, if the signal 524 is kept at the logic high level for apredetermined time period (e.g., a predetermined number of clockcycles), the counter component 514 outputs the OTP-detection signal 208(e.g., at the logic high level) to trigger the OTP protection.

Combining Equation 5 and Equation 8, the condition for OTP protection isdetermined as follows, according to some embodiments:

$\begin{matrix}{{\frac{R_{T} \times R_{OVP}}{R_{OVP} + R_{T}} \times \Delta\; I_{OTP}} < V_{REF}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$where ΔI_(OTP) represents a change of the current 186 between the firsttime period (e.g., the time period T_(S0)) and the second time period(e.g., the time period T_(S1)). For example, when the temperature of thepower conversion system 100 is higher than the temperature threshold,the resistance of the resistor 114 (i.e., R_(OVP)) is much larger thanthe resistance of the resistor 118 (i.e., R_(T)). The condition for OTPprotection is determined as follows, according to certain embodiments:R _(T) ×ΔI _(OTP) <V _(REF)  (Equation 10)

FIG. 7 is a simplified diagram showing certain components of the OVPdetector 318 as part of the detection component 202 in the powerconversion system 100 according to one embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 7, the OVP detector 318 includes current sources 602, 608 and 618,transistors 604, 610 and 616, resistors 606 and 612, a capacitor 614, aSchmitt trigger component 620, and a counter component 622. For example,the resistance of the resistor 612 is equal to the resistance of theresistor 606 times a predetermined parameter K (e.g., K>1, or K≤1).

According to one embodiment, the current source 602 is configured toprovide a current 624 (e.g., I₁) to flow through the resistor 606, andthe current source 608 is configured to provide another current 626(e.g., I₂). For example, the current 624 and the current 626 are equalin magnitude to a reference current (e.g., I_(ref)). In another example,the current 624 and the current 626 are not equal in magnitude.

According to another embodiment, when the switch 314 is closed during afirst time period (e.g., the time period T_(OVP)), the terminal 130 isconfigured to provide the current 188 to flow through the resistor 606.For example, under certain circumstances, the voltage signal 184 isequal in magnitude to a voltage 630 (e.g., V_(R1)) associated with theresistor 606 and/or a voltage 632 (e.g., V_(R2)) associated with theresistor 612, as follows:V ₁ =V _(R1)=(I ₁ +I _(OVP))×R ₁=(I _(ref) +I _(OVP))×R ₁V ₁ =V _(R2) =I ₂ ×R ₂ =I _(ref) ×K×R ₁  (Equation 11)where V_(R1) represents the voltage signal 630, I₁ represents thecurrent 624, I_(OVP) represents the current 188, and R₁ represents theresistance of the resistor 606. In addition, V_(R2) represents thevoltage signal 632, I₂ represents the current 626, R₂ represents theresistance of the resistor 612, and I_(ref) represents the referencecurrent.

In another example, the voltage 630 (e.g., V_(R1)) is equal to thevoltage 632 (e.g., V_(R2)) in magnitude. In one embodiment, if thevoltage signal 142 increases in magnitude, the current 188 increases inmagnitude, and the voltage signal 630 (e.g., V_(R1)) increases inmagnitude. In another embodiment, if the voltage signal 142 increases inmagnitude, the voltage 632 (e.g., V_(R2)) also increases in magnitude,and the current 628 increases in magnitude. As an example, if thevoltage signal 630 (e.g., V_(R1)) exceeds a first voltage threshold, thecurrent 628 becomes larger in magnitude than the current 626 provided bythe current source 608. The capacitor 614 begins to discharge to providea current 636 flowing through the transistor 610 and the resistor 612,according to certain embodiments. For example, the voltage 634 (e.g.,V_(F)) decreases in magnitude. As an example, if the voltage 634 (e.g.,V_(F)) becomes smaller than a second voltage threshold, the transistor616 is turned off, in certain embodiments. In another example, an inputsignal 640 that is associated with the transistor 616 and a bias current644 provided by the current source 618 increases in magnitude. In yetanother example, the resistor R1 is chosen so that the voltage signal630 (e.g., V_(R1)) is smaller in magnitude than a forward voltage of thediode 116.V _(R1)=(I ₁ +I _(OVP))×R ₁ <V _(f)  (Equation 12)where V_(f) represents the forward voltage of the diode 116.

According to yet another embodiment, the Schmitt trigger component 620is configured to receive the input signal 640 and generate a signal 642.For example, if the input signal 640 is smaller in magnitude than afirst predetermined threshold, the Schmitt trigger component 620 isconfigured to output the signal 642 at a logic low level. On the otherhand, if the input signal 640 becomes higher in magnitude than a secondpredetermined threshold as the voltage 634 (e.g., V_(F)) decreases inmagnitude, the Schmitt trigger component 620 is configured to output thesignal 642 at a logic high level. In another example, if the signal 642is kept at the logic high level for a predetermined time period (e.g., apredetermined number of clock cycles), the counter component 622 outputsthe OVP-detection signal 210 (e.g., at the logic high level) to triggerthe OVP protection. Combining Equation 2 and Equation 11, the conditionfor OVP detection is determined as follows, according to certainembodiments:V _(o)=(K−1)×I _(ref) ×R _(OVP) +I _(ref) ×K×R ₁  (Equation 13)where V_(o) represents the voltage signal 142 associated with theauxiliary winding 108. For example, the voltage signal 142 is related tothe output voltage 198 as below.

$\begin{matrix}{V_{o} = {\frac{N_{aux}}{N_{\sec}} \times V_{out}}} & \left( {{Equation}\mspace{14mu} 14} \right)\end{matrix}$where V_(out) represents the output voltage 198, and N_(aux)/N_(sec)represents a turns ratio between the auxiliary winding 108 and thesecondary winding 106.

According to one embodiment, a system controller for protecting a powerconversion system includes, a first controller terminal configured toprovide a drive signal to close and open a switch to affect a firstcurrent flowing through a primary winding of a power conversion system,the drive signal being associated with one or more switching periodsincluding one or more first switching periods and one or more secondswitching periods, and a second controller terminal configured toreceive one or more first input signals during the one or more firstswitching periods and receive one or more second input signals duringthe one or more second switching periods. The system controller isconfigured to, process information associated with the first inputsignals, determine whether a temperature associated with the powerconversion system is larger than a predetermined temperature thresholdbased on at least information associated with the first input signals,and in response to the temperature associated with the power conversionsystem being larger than the predetermined temperature threshold,generate the drive signal to cause the switch open and remain open toprotect the power conversion system. The system controller is furtherconfigured to, process information associated with the second inputsignals, determine whether an output voltage associated with a secondarywinding of the power conversion system is larger than a predeterminedvoltage threshold based on at least information associated with thesecond input signals, and in response to the output voltage associatedwith the secondary winding of the power conversion system being largerthan the predetermined voltage threshold, generate the drive signal tocause the switch to open and remain open to protect the power conversionsystem. For example, the system controller is implemented according toFIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, and/or FIG. 7.

According to another embodiment, a system for protecting a powerconversion system includes, a system controller including a firstcontroller terminal configured to provide a drive signal to close andopen a switch to affect a first current flowing through a primarywinding of a power conversion system, and a second controller terminalconfigured to receive one or more input signals, the power conversionsystem further including a secondary winding and an auxiliary winding,the primary winding coupled to the secondary winding, a first resistorincluding a first resistor terminal and a second resistor terminal, thefirst resistor terminal being coupled to the second controller terminal,one or more first diodes including a first diode terminal and a seconddiode terminal, a first diode terminal being coupled to the secondcontroller terminal, and a second resistor including a third resistorterminal and a fourth resistor terminal, the third resistor terminalbeing coupled to the second diode terminal. The second resistor terminalis configured to receive an output signal associated with the auxiliarywinding coupled to the secondary winding. For example, the system isimplemented according to at least FIG. 2, FIG. 4, and/or FIG. 7.

According to yet another embodiment, a system controller for protectinga power conversion system includes, a first controller terminalconfigured to provide a drive signal to close and open a switch toaffect a first current flowing through a primary winding of a powerconversion system, the drive signal being associated with one or moreswitching periods including a first switching period and a secondswitching period; and a protection component configured to receive afirst voltage signal associated with a first input current flowingthrough a resistor during the first switching period and receive asecond voltage signal associated with a second input current flowingthrough the resistor during the second switching period, the first inputcurrent and the second input current being different in magnitude. Theprotection component is further configured to, in response to adifference between the first voltage signal and the second voltagesignal being larger than a predetermined threshold in magnitude, outputa protection signal to generate the drive signal to cause the switch toopen and remain open to protect the power conversion system. Forexample, the system controller is implemented according to at least FIG.4, FIG. 5, and/or FIG. 6.

According to yet another embodiment, a system controller for protectinga power conversion system includes, a first controller terminalconfigured to receive an input current, a first resistor configured toreceive a first current and the input current and generate a firstvoltage based on at least information associated with the first currentand the input current, a second resistor configured to receive a secondcurrent and generate a second voltage based on at least informationassociated with the second current, and a processing componentconfigured to, in response to the first voltage becoming larger than afirst voltage threshold in magnitude, increase the second voltage inmagnitude, discharge a capacitor coupled to the processing component,and decrease a third voltage in magnitude associated with the capacitor.For example, the system controller is implemented according to at leastFIG. 7.

In one embodiment, a method for protecting a power conversion systemincludes, providing a drive signal to close and open a switch to affecta first current flowing through a primary winding of a power conversionsystem, the drive signal being associated with one or more switchingperiods including one or more first switching periods and one or moresecond switching periods, receiving one or more first input signalsduring the one or more first switching periods, processing informationassociated with the one or more first input signals, and determiningwhether a temperature associated with the power conversion system islarger than a predetermined temperature threshold based on at leastinformation associated with the one or more first input signals. Themethod further includes, in response to the temperature associated withthe power conversion system being larger than the predeterminedtemperature threshold, generating the drive signal to cause the switchopen and remain open to protect the power conversion system, receivingone or more second input signals during the one or more second switchingperiods, processing information associated with the one or more secondinput signals, determining whether an output voltage associated with asecondary winding of the power conversion system is larger than apredetermined voltage threshold based on at least information associatedwith the one or more second input signals, and in response to the outputvoltage associated with the secondary winding of the power conversionsystem being larger than the predetermined voltage threshold, generatingthe drive signal to cause the switch to open and remain open to protectthe power conversion system. For example, the method is implementedaccording to FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 6, and/or FIG. 7.

In another embodiment, a method for protecting a power conversion systemincludes, providing a drive signal to close and open a switch to affecta first current flowing through a primary winding of a power conversionsystem, the drive signal being associated with one or more switchingperiods including a first switching period and a second switchingperiod, receiving a first voltage signal associated with a first inputcurrent flowing through a resistor during the first switching period,receiving a second voltage signal associated with a second input currentflowing through the resistor during the second switching period, thefirst input current and the second input current being different inmagnitude, and in response to a difference between the first voltagesignal and the second voltage signal being larger than a predeterminedthreshold in magnitude, outputting a protection signal to generate thedrive signal to cause the switch to open and remain open to protect thepower conversion system. For example, the method is implementedaccording to at least FIG. 4, FIG. 5, and/or FIG. 6.

In yet another embodiment, a method for protecting a power conversionsystem includes, receiving an input current and a first current,processing information associated with the input current and the firstcurrent, and generating a first voltage based on at least informationassociated with the first current and the input current. The methodadditionally includes, receiving a second current, processinginformation associated with the second current, and generating a secondvoltage based on at least information associated with the secondcurrent. The method further includes, in response to the first voltagebecoming larger than a first voltage threshold in magnitude, increasingthe second voltage in magnitude, discharging a capacitor, and decreasinga third voltage in magnitude associated with the capacitor. For example,the method is implemented according to at least FIG. 7.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for protecting a powerconversion system, the system controller comprising: a first controllerterminal configured to provide a drive signal to close and open a switchto affect a first current flowing through a primary winding of a powerconversion system, the drive signal being associated with one or moreswitching periods including a first switching period, a second switchingperiod, and a third switching period; and a second controller terminalconfigured to receive a first input signal during the first switchingperiod, receive a second input signal during the second switchingperiod, and receive a third input signal during the third switchingperiod; wherein: the first switching period includes a first start timeand a first end time; the second switching period includes a secondstart time and a second end time; and the third switching periodincludes a third start time and a third end time; wherein: the first endtime of the first switching period precedes the second start time of thesecond switching period; and the second end time of the second switchingperiod precedes the third start time of the third switching period;wherein the system controller is configured to: process informationassociated with the first input signal received during the firstswitching period and the third input signal received during the thirdswitching period; determine whether a temperature associated with thepower conversion system is larger than a predetermined temperaturethreshold based on at least information associated with the first inputsignal and the third input signal; and in response to the temperatureassociated with the power conversion system being larger than thepredetermined temperature threshold, generate the drive signal to causethe switch to open and remain open to protect the power conversionsystem; wherein the system controller is further configured to: processinformation associated with the second input signal; determine whetheran output voltage associated with a secondary winding of the powerconversion system is larger than a predetermined voltage threshold basedon at least information associated with the second input signal; and inresponse to the output voltage associated with the secondary winding ofthe power conversion system being larger than the predetermined voltagethreshold, generate the drive signal to cause the switch to open andremain open to protect the power conversion system; wherein the secondcontroller terminal is further configured to: receive the first inputsignal during only a first part of the first switching period; receivethe second input signal during only a second part of the secondswitching period; and receive the third input signal during only a thirdpart of the third switching period; wherein: the first part is smallerin magnitude than the first switching period, the first part starting atthe first start time of the first switching period and ending before thefirst end time of the first switching period; the second part is smallerin magnitude than the second switching period, the second part startingat the second start time of the second switching period and endingbefore the second end time of the second switching period; and the thirdpart is smaller in magnitude than the third switching period, the thirdpart starting at the third start time of the third switching period andending before the third end time of the third switching period.
 2. Thesystem controller of claim 1 is further configured to, in response tothe output voltage associated with the secondary winding of the powerconversion system being larger than the predetermined voltage thresholdto, generate the drive signal to cause the switch to be opened withoutany modulation.
 3. The system controller of claim 1 is furtherconfigured to, in response to the output voltage associated with thesecondary winding of the power conversion system being larger than thepredetermined voltage threshold to, generate the drive signal to causethe switch to remain open for a first period of time larger in durationthan one of the second switching periods.
 4. The system controller ofclaim 1 wherein: the second controller terminal is coupled to a firstresistor terminal of a first resistor, the first resistor furtherincluding a second resistor terminal; the second controller terminal iscoupled to a first diode terminal of one or more first diodes, the oneor more first diodes further including a second diode terminal; thesecond diode terminal is coupled to a third resistor terminal of asecond resistor, the second resistor further including a fourth resistorterminal; and the second resistor terminal is configured to receive anoutput signal associated with an auxiliary winding coupled to thesecondary winding.
 5. The system controller of claim 4 wherein thesecond resistor is a thermal resistor associated with a resistancechanging with temperature.
 6. The system controller of claim 5 whereinthe resistance decreases with increasing temperature.
 7. The systemcontroller of claim 4 wherein: the first diode terminal is an anodeterminal; and the second diode terminal is a cathode terminal.
 8. Thesystem controller of claim 1, further comprising: a third controllerterminal configured to receive a supply voltage; a fourth controllerterminal configured to receive a bias voltage; a fifth controllerterminal configured to receive a current-sensing signal related to thefirst current flowing through the primary winding; and a sixthcontroller terminal configured to receive a feedback signal related tothe output voltage.
 9. The system controller of claim 8 wherein thesystem controller includes no other terminals.
 10. The system controllerof claim 8 wherein the first controller terminal, the second controllerterminal, the third controller terminal, the fourth controller terminal,the fifth controller terminal, and the sixth controller terminal are sixdifferent pins respectively.
 11. A system for protecting a powerconversion system, the system comprising: a system controller includinga first controller terminal configured to provide a drive signal toclose and open a switch to affect a first current flowing through aprimary winding of a power conversion system, and a second controllerterminal configured to receive one or more input signals, the powerconversion system further including a secondary winding and an auxiliarywinding, the primary winding coupled to the secondary winding; a firstresistor including a first resistor terminal and a second resistorterminal, the first resistor terminal being directly coupled to thesecond controller terminal; one or more first diodes including a firstdiode terminal and a second diode terminal, a first diode terminal beingcoupled to the second controller terminal; and a second resistorincluding a third resistor terminal and a fourth resistor terminal, thethird resistor terminal being coupled to the second diode terminal;wherein the second resistor terminal is directly coupled to theauxiliary winding and is configured to receive an output signalassociated with the auxiliary winding coupled to the secondary winding.12. The system of claim 11 wherein the second resistor is a thermalresistor associated with a resistance changing with temperature.
 13. Thesystem of claim 12 wherein the resistance decreases with increasingtemperature.
 14. The system of claim 11 wherein: the first diodeterminal is an anode terminal; and the second diode terminal is acathode terminal.
 15. The system of claim 11 wherein the systemcontroller further includes: a third controller terminal configured toreceive a supply voltage; a fourth controller terminal configured toreceive a bias voltage; a fifth controller terminal configured toreceive a current-sensing signal related to the first current flowingthrough the primary winding; and a sixth controller terminal configuredto receive a feedback signal related to an output signal associated withthe secondary winding.
 16. The system of claim 15 wherein the systemcontroller includes no other terminals.
 17. The system of claim 15wherein the first controller terminal, the second controller terminal,the third controller terminal, the fourth controller terminal, the fifthcontroller terminal, and the sixth controller terminal are six differentpins respectively.
 18. A system controller for protecting a powerconversion system, the system controller comprising: a first controllerterminal configured to provide a drive signal to close and open a switchto affect a first current flowing through a primary winding of a powerconversion system, the drive signal being associated with one or moreswitching periods including a first switching period and a secondswitching period; and a protection component configured to receive afirst voltage signal associated with a first input current flowingthrough a resistor during the first switching period and receive asecond voltage signal associated with a second input current flowingthrough the resistor during the second switching period, the first inputcurrent and the second input current being different in magnitude;wherein the protection component is further configured to, in responseto the first voltage signal minus the second voltage signal beingsmaller than a predetermined threshold in magnitude, generate an outputsignal for generating the drive signal to cause the switch to open andremain open; wherein: the first switching period includes a first starttime and a first end time; and the second switching period includes asecond start time and a second end time; wherein the first end time ofthe first switching period precedes the second start time of the secondswitching period; wherein: the first input current is not equal to zeroin magnitude; and the second input current is not equal to zero inmagnitude; wherein the first voltage signal minus the second voltagesignal is proportional to the first input current minus the second inputcurrent.
 19. The system controller of claim 18, further comprising asecond controller terminal coupled to one or more diodes configured toreceive the first input current and receive the second input current.20. The system controller of claim 18 wherein the protection componentis further configured to receive the first voltage signal during only afirst part of the first switching period.
 21. The system controller ofclaim 18 wherein the protection component is further configured toreceive the second voltage signal during only a second part of thesecond switching period.
 22. The system controller of claim 18 whereinthe protection component is further configured to, in response to thefirst voltage signal minus the second voltage signal being smaller thanthe predetermined threshold in magnitude, generate the output signal forgenerating the drive signal to cause the switch to be opened without anymodulation.
 23. The system controller of claim 18 wherein the protectioncomponent is further configured to, in response to the first voltagesignal minus the second voltage signal being smaller than thepredetermined threshold in magnitude, generate the output signal forgenerating the drive signal to cause the switch to remain open for aperiod of time larger in duration than the first switching period. 24.The system controller of claim 18 wherein the second switching period isseparated from the first switching period by one or more third switchingperiods.
 25. The system controller of claim 18 wherein the secondswitching period immediately follows the first switching period.
 26. Thesystem controller of claim 18 wherein the protection component includes:a first current-source component configured to provide the first inputcurrent; and a second current-source component configured to provide thesecond input current.
 27. The system controller of claim 18 wherein thepredetermined threshold is larger in magnitude than zero.
 28. A systemcontroller for protecting a power conversion system, the systemcontroller comprising: a first controller terminal configured to receivean input current; a first resistor configured to receive a first currentand the input current and generate a first voltage based on at leastinformation associated with the first current and the input current; asecond resistor configured to receive a second current and generate asecond voltage based on at least information associated with the secondcurrent; and a processing component configured to, in response to thefirst voltage becoming larger than a first voltage threshold inmagnitude, increase the second voltage in magnitude, discharge acapacitor coupled to the processing component, and decrease a thirdvoltage in magnitude associated with the capacitor; wherein: the firstresistor includes a first resistor terminal and a second resistorterminal, the first voltage being generated at the first resistorterminal; the second resistor includes a third resistor terminal and afourth resistor terminal, the second voltage being generated at thethird resistor terminal; and the first resistor terminal is not directlycoupled to the third resistor terminal.
 29. The system controller ofclaim 28 wherein the first voltage is equal in magnitude to the secondvoltage.
 30. A method for protecting a power conversion system, themethod comprising: providing a drive signal to close and open a switchto affect a first current flowing through a primary winding of a powerconversion system, the drive signal being associated with one or moreswitching periods including a first switching period, a second switchingperiod, and a third switching period; receiving a first input signalduring the first switching period, receiving a second input signalduring the second switching period, and receiving a third input signalduring the third switching period; wherein: the first switching periodincludes a first start time and a first end time; the second switchingperiod includes a second start time and a second end time; and the thirdswitching period includes a third start time and a third end time;wherein: the first end time of the first switching period precedes thesecond start time of the second switching period; and the second endtime of the second switching period precedes the third start time of thethird switching period; processing information associated with the firstinput signal received during the first switching period and the thirdinput signal received during the third switching period; determiningwhether a temperature associated with the power conversion system islarger than a predetermined temperature threshold based on at leastinformation associated with the first input signal and the third inputsignal; in response to the temperature associated with the powerconversion system being larger than the predetermined temperaturethreshold, generating the drive signal to cause the switch to open andremain open to protect the power conversion system; processinginformation associated with the second input signal; determining whetheran output voltage associated with a secondary winding of the powerconversion system is larger than a predetermined voltage threshold basedon at least information associated with the second input signal; and inresponse to the output voltage associated with the secondary winding ofthe power conversion system being larger than the predetermined voltagethreshold, generating the drive signal to cause the switch to open andremain open to protect the power conversion system; wherein: the processof receiving a first input signal during the first switching periodinclude receiving the first input signal during only a first part of thefirst switching period; the process of receiving a second input signalduring the second switching period includes receiving the second inputsignal during only a second part of the second switching period; and theprocess of receiving a third input signal during the third switchingperiod includes receiving the third input signal during only a thirdpart of the third switching period; wherein: the first part is smallerin magnitude than the first switching period, the first part starting atthe first start time of the first switching period and ending before thefirst end time of the first switching period; the second part is smallerin magnitude than the second switching period, the second part startingat the second start time of the second switching period and endingbefore the second end time of the second switching period; and the thirdpart is smaller in magnitude than the third switching period, the thirdpart starting at the third start time of the third switching period andending before the third end time of the third switching period.
 31. Amethod for protecting a power conversion system, the method comprising:providing a drive signal to close and open a switch to affect a firstcurrent flowing through a primary winding of a power conversion system,the drive signal being associated with one or more switching periodsincluding a first switching period and a second switching period;receiving a first voltage signal associated with a first input currentflowing through a resistor during the first switching period; receivinga second voltage signal associated with a second input current flowingthrough the resistor during the second switching period, the first inputcurrent and the second input current being different in magnitude; andin response to the first voltage signal minus the second voltage signalbeing smaller than a predetermined threshold in magnitude, generating anoutput signal for generating the drive signal to cause the switch toopen and remain open; wherein: the first switching period includes afirst start time and a first end time; and the second switching periodincludes a second start time and a second end time; wherein the firstend time of the first switching period precedes the second start time ofthe second switching period; wherein: the first input current is notequal to zero in magnitude; and the second input current is not equal tozero in magnitude; wherein the first voltage signal minus the secondvoltage signal is proportional to the first input current minus thesecond input current.
 32. A method for protecting a power conversionsystem, the method comprising: receiving an input current and a firstcurrent; processing information associated with the input current andthe first current; generating at a first resistor a first voltage basedon at least information associated with the first current and the inputcurrent; receiving a second current; processing information associatedwith the second current; generating at a second resistor a secondvoltage based on at least information associated with the secondcurrent; and in response to the first voltage becoming larger than afirst voltage threshold in magnitude, increasing the second voltage inmagnitude; discharging a capacitor, and decreasing a third voltage inmagnitude associated with the capacitor, wherein: the first resistorincludes a first resistor terminal and a second resistor terminal, thefirst voltage being generated at the first resistor terminal; the secondresistor includes a third resistor terminal and a fourth resistorterminal, the second voltage being generated at the third resistorterminal; and the first resistor terminal is not directly coupled to thethird resistor terminal.